A hot water boiler comprises an integral part of a heating system of a building structure and is used to heat a fluid, such as water, circulating at high temperatures through hydronic piping and radiator/convector heating systems. Gaseous or liquid fuels are ignited within the boiler to generate heat which is transferred to the circulating water which is completely isolated from the outside environment. The heated water exits the boiler, transfers the heat throughout the building, and returns to the boiler for reheating. The spent combustion gas is exhausted into the atmosphere.
One type of boiler, referred to as a "modified Scotch boiler" in the present assignee's U.S. Pat. No. 4,838,210 issued to Kirby, has a burner which is located at the front of the boiler, combusts fuel within a horizontally-disposed fire-tube, and forces the combustion gases toward the rear of the boiler in a first pass. At the rear of the boiler, a fire reversing chamber reverses the flow of the gases toward the front of the boiler through a set of second pass fire-tubes located above the first pass fire-tube. The combustion gases travel back to the rear of the boiler in third pass fire-tubes, and then, are exhausted into the atmosphere. The Kirby patent discloses lining a back portion of the reversing chamber with a replaceable, one-piece, refractory liner.
U.S. Pat. Nos.: 3,848,573 issued to Phillips; 4,195,596 issued to Scheifley et al.; 5,029,557 issued to Korenberg; 4,860,695 issued to Korenberg; 4,920,925 issued to Korenberg et al.; and 4,989,549 issued to Korenberg disclose examples of other boilers having a first pass fire-tube, at least one reversing chamber, and a second pass fire-tube bundle.
Many forces acting on such boilers can reduce the life of the boilers. For instance, thermal shocking of boiler heating surfaces can result from the introduction of cold system return water into a hot boiler. Some boiler designers attempt to prevent thermal shocking by utilizing bypass circulation systems as disclosed in U.S. Pat. Nos.: 5,590,832 issued to Fiedrich; 2,557,368 issued to Broderick; 2,262,194 issued to Newton; and 3,168,243 issued to Porland. Other examples of detrimental forces which can reduce the life of a boiler include the stress and strain concentrated on the weld joints of the boiler frame due to unequal expansion of different boiler components and excess radiant heat within the boiler exposed to various weld joints of the boiler.
Although various ones of the above-referenced boilers may be satisfactory for their intended purposes, there is a need for an improved boiler construction capable of withstanding the various thermal forces acting on the boiler such as, thermal shocking, to prolong the life of the boiler. The boiler should optimize combustion, increase heat transfer, and operate efficiently, and the boiler manufacturing and installation costs should provide savings over existing boiler designs.